This process points to Microsoft's product called Windows Defender. This security product serves as a defense against spyware and unwanted software. Upgrades to the product made it less intensive when running locally on a computer. Windows Defender allows the user to run a quick scan or a full scan of the computer. Additionally the product provides the facility of running a custom scan within a specified repository. The process should never be closed off through the Task Manager; instead it can be simply removed by closing the application itself. As with any other malware/virus detector, the application needs to be updated regularly to utilize the latest of virus/spyware definitions. This can be done manually through the Update section of the product.

The main functions of the msmpeng.exe file include the ability to remove, quarantine, and prevent spyware infections. Apart from scanning for spyware, the msmpeng.exe file also searches for worms and trojans.

The framework of the msmpeng.exe file was based on the GIANT Antispyware, a product of GIANT Company Software, Inc. Apart from scanning, Windows Defender also includes various real-time Security agents used to check areas of Windows that can contain unsafe programs. ActiveX applications can also be removed by the msmpeng.exe file.
Non-system processes like msmpeng.exe originate from software you installed on your system. Since most applications store data on your hard disk and in your system's registry, it is likely that your computer has suffered fragmentation and accumulated invalid entries which can affect your PC's performance.

In Windows Task Manager, you can see what CPU, memory, disk and network utilization is causing the Microsoft Windows Defender Antispyware process. To access the Task Manager, hold down the Ctrl + Shift + Esc keys at the same time. These three buttons are located on the far left of your keyboard.

This process is considered safe. It is unlikely to pose any harm to your system. The msmpeng.exe file should be located in the folder C:\Program Files\Windows Defender. Otherwise it could be a Trojan.

This process is not considered CPU intensive. However, running too many processes on your system may affect your PC’s performance. To reduce system overload, you can use the Microsoft System Configuration Utility (MSConfig) or the Windows Task Manager to manually find and disable processes that launch upon start-up.

Use the Windows Resource Monitor to find out which processes and applications write/read the most on the hard drive, send the most data to the Internet, or use the most memory. To access the Resource Monitor, press the key combination Windows key + R and then enter 'resmon'.